1. Field of the Invention
This invention relates to pedal cranks and pedal crank drive mechanisms for stationary and transportation bicycle applications and claims benefit of prior filed copending Provisional Application No. 60/126,491, filed Mar. 25, 1999.
2. Background of the Invention
Bicycles, both transportation and stationary, have traditionally included pedal cranks of a fixed length wherein the pedal rotates around the axle in a circular path determined by the length of the pedal crank. However, due to the physiology of the human body, this circular path fails to maximize the biomechanical forces of the legs of the person pedaling the bicycle. This results in wasted energy, fatigue, and excessive wear on the knees, and ankles.
In addition, many people use bicycles, and particularly stationary bicycles as a means of obtaining a cardiovascular workout or for rehabilitation purposes following an injury. It has been found, however, that a full cardiovascular benefit is not achieved due to the fact that the leg muscles of the user prematurely fatigue requiring the user to rest. In the case of rehabilitation after an injury, a particular muscle group or joint, such as the top of the thigh or knee fatigue or become sore before maximum benefit is achieved.
A need, therefore, exists for a pedal crank that matches the biomechanical forces of the human legs such that less energy is expended allowing all used muscle groups to fatigue at a more even rate after the maximum cardiovascular benefit for that exercise is achieved.
Devices for varying the length or altering the path of the pedal crank have been tried with little success. Such devices are either too heavy or cumbersome or cannot withstand the stresses resulting from the required repetitive motion. A need, therefore, also exists for a pedal crank that alters the path of travel from traditional fixed length pedals which is strong enough to endure heavy use without being heavy or cumbersome.
The pedal crank of the present invention is capable of extension to a maximum length which corresponds to the range of maximum biomechanical force applied by the leg of the user to the pedal of an exercise machine. The pedal crank then retracts in length on rotation to a point corresponding to the minimum biomechanical force. In this way, the maximum benefit is achieved while leg/knee stress is reduced over the range of motion when compared to traditional fixed length pedal cranks.
It has been found that the pedal energy expended by a user of the pedal crank of the present invention is 15% less than the energy expended by a user of a pedal crank of fixed length. In this way, leg stress and fatigue is reduced allowing the user to obtain a longer, more extensive cardiovascular workout at a higher or sustained heart rate because leg fatigue is substantially reduced.
The pedal crank assembly of the present invention includes, generally, a cam, hub, arm, cam follower, and a pair of rods. The pedal crank may be used with different types of exercise machines which turn a central rotating shaft. Such machines primary include bicycles, stationary and ambulatory, but also may include other devices such as elliptical machines.
The cam is secured to the exercise machine and includes a channel therein. The channel may be annular or may be of another geometry where a different path of travel is desired.
The cam also includes a hole for the shaft of the exercise machine to extend through This hole may be eccentric from the center point of the channel or concentric.
The arm includes the pedal or other force applying member of the exercise machine. The cam follower engages the channel in the cam and travels therein. The cam follower is operable with the arm such that as the arm is driven by the face applied to the pedal or other such member, the arm drives the cam follower within the channel.
A pair of rods extend from the hub to the arm. Each rod has a length such that the distance between the hub and the arm is varied by the length of the rods.
In a first preferred embodiment, the rods are fixed in the arm at their first end. Channels are machined through the hub to receive the second end of the rods such that the rods are capable of reciprocating within the channels.
As the arm drives the cam follower around the channel in the cam, the eccentric hole in the cam through which the shaft extends causes the distance between the arm and the hub to vary. The rods thus reciprocate within the channels of the hub and also rotate the hub, and therefore, the shaft. A linear bearing is inserted in the channels of the hub in which the rods reciprocate.
In a second preferred embodiment, the second ends of the rods are fixed in the hub. Channels are cut in the arm to receive the first ends of the rods. The rods thus reciprocate within the channels of the arm as the assembly is rotated. A linear bearing is inserted in the channels of the arm between the arm and the rods.
In a third preferred embodiment, the cam includes a ring with a plate inside. The plate is round such that the ring rotates around the circumference of the plate when the plate is fixed to the exercise machine. A plurality of roller bearings are fixed within the ring to rotate around the circumference of the plate.
The plate includes an eccentric hole to receive the shaft of the exercise machine. A hub is fixed to the shaft and capable of rotation therewith. The arm, cam follower and rods are configured as described above with regard to the first and second preferred embodiment with the exception that the cam follower is fixed within a hole in the ring. In this embodiment, the cam follower rotates the ring around the plate. The fact that the hole in the plate is eccentric causes the distance between the hole and the hole in the ring to change as the ring rotates around the plate. This distance change causes the rods to reciprocate within either the hub or the arm depending upon which includes the channels.
It is an object of the present invention to provide a pedal crank that maximizes the biomechanical forces of the human leg preventing localized premature fatigue of specific muscle groups thereby allowing a more complete workout for the same expended energy.
It is a further object of the present invention to provide such a pedal crank which varies in length over its rotation.
Another object of the present invention is to provide such a pedal crank which is light in weight, cost effective to manufacture yet durable enough to withstand heavy use.
Other objects and advantages of the invention will become apparent upon reading the following detailed description and upon reference to the drawings.